The technical field of the invention pertains generally to intermodal chassis designs, and, more particularly, to improvements in an intermodal chassis especially suited for 53 foot domestic use intermodal containers and that provides for improvements in load capacity and ease of use, while meeting state specific transportation regulations.
Intermodal chassis are semi-trailers used for hauling intermodal shipping containers over the road. Intermodal shipping containers are used for shipping product via road, rail, or ocean. The 53 foot (53′) shipping container is also referred to as a “long box” shipping container, or a “high cube” container because it provides expansive capacity with a typical height of (9′6″) 114″, width of (8′6″) 102″, and length of 53′. This is 1 foot taller than standard height containers. Another common container length is 48′. International shipments typically utilize intermodal containers that are 6″ narrower and typically either 20′ or 40′ in length.
The 53′ intermodal long box container is the most common type of container used for domestic shipping within the United States. The 53′ container was constructed and introduced primarily for domestic over-the-road/highway and railroad shipping. 53′ containers are typically constructed of 14-gauge (14 Ga) corrugated steel throughout, with 1⅛″ thick marine plywood flooring on the interior.
A typical intermodal chassis for a 53′ container consists of front and rear bolsters which engage with the lower edges at the front and rear of the container, with a frame extending between and interconnecting the front and rear bolsters, tandem axles positioned toward the rear of the chassis, and a forward portion of the chassis near the front bolster that has a raised surface section sized to fit within a corresponding tunnel depression (3⅛″ deep) section on the underside of the container. The typical intermodal chassis is constructed of steel, with a standard leaf spring type suspension, standard sized steel hub wheels (8¼″×22.5″ hub), and standard sized tires (11R22.5 tire). The kingpin for connection with the fifth wheel of a towing tractor is typically set back from the rear face of the bolster by 36″.
The 53′ long box/high cube containers typically require careful loading arrangements to achieve load balancing and distribution between the front nose of the container and locations within the container forward of the chassis tandems, in order to meet particular state highway transportation regulations (or so-called bridge laws). For example, FIG. 1 shows a side view 100 of a typical truck 104 and semi-trailer 102 loading arrangement for meeting California Department of Transportation regulations. The kingpin-to-rear-axle (KPRA) length 108 must not exceed a length of 40 feet. Commercial vehicles may not exceed 80 k lbs GVW. Axle restrictions include a limit of 34 k lbs on the drive tires 112, 34 k lbs on the tandem tires 114, and 12 k lbs on the steer tires 110. To meet these requirements, the typical semi-trailer 102 needs to have cargo 106 arranged to be secured forward of the rear tandems 114, keeping product between the tandem axles 114 and the nose or front of the container. Carriers are advised to load heavier pallets in the nose of the container closer to the tractor cab 104, followed by light pallets and then the lightest pallets rearward, yet still forward of the rear most axle. As shown in FIG. 1, the result is empty (unused/unusable) space in the container aft of the rear tandems 114. Moreover, substantial effort and care is needed to distribute the weight within the container from left side to right side and from the nose of the container space to the rear most position of pallets and product, often using inflatable air bags or other dunnage (not shown) to stabilize separation and spacing of pallets and product. Because loads need to be scaled at the origin of a particular route (to ensure the load is legal for the destination state), considerable care is needed to properly load the cargo 106 into the trailer 102.
What is needed, therefore, are improved intermodal chassis designs that provide for improvements in load capacity, cost of operation, and ease of use, and that adhere to state specific transportation regulations such as those established by the California Department of Transportation that apply to over highway shipping using 53′ intermodal containers.
The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention taken in conjunction with the accompanying drawings.